read_preferences
– Utilities for choosing which member of a replica set to read from.¶
Utilities for choosing which member of a replica set to read from.
-
class
pymongo.read_preferences.
Primary
¶ Primary read preference.
- When directly connected to one mongod queries are allowed if the server is standalone or a replica set primary.
- When connected to a mongos queries are sent to the primary of a shard.
- When connected to a replica set queries are sent to the primary of the replica set.
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document
¶ Read preference as a document.
-
mode
¶ The mode of this read preference instance.
-
name
¶ The name of this read preference.
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class
pymongo.read_preferences.
PrimaryPreferred
(tag_sets=None, max_staleness=-1)¶ PrimaryPreferred read preference.
- When directly connected to one mongod queries are allowed to standalone servers, to a replica set primary, or to replica set secondaries.
- When connected to a mongos queries are sent to the primary of a shard if available, otherwise a shard secondary.
- When connected to a replica set queries are sent to the primary if available, otherwise a secondary.
Parameters: - tag_sets: The
tag_sets
to use if the primary is not available. - max_staleness: (integer, in seconds) The maximum estimated length of time a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations. Default -1, meaning no maximum. If it is set, it must be at least 90 seconds.
-
document
¶ Read preference as a document.
-
max_staleness
¶ The maximum estimated length of time (in seconds) a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations, or -1 for no maximum.
-
min_wire_version
¶ The wire protocol version the server must support.
Some read preferences impose version requirements on all servers (e.g. maxStalenessSeconds requires MongoDB 3.4 / maxWireVersion 5).
All servers’ maxWireVersion must be at least this read preference’s min_wire_version, or the driver raises
ConfigurationError
.
-
mode
¶ The mode of this read preference instance.
-
mongos_mode
¶ The mongos mode of this read preference.
-
name
¶ The name of this read preference.
-
tag_sets
¶ Set
tag_sets
to a list of dictionaries like [{‘dc’: ‘ny’}] to read only from members whosedc
tag has the value"ny"
. To specify a priority-order for tag sets, provide a list of tag sets:[{'dc': 'ny'}, {'dc': 'la'}, {}]
. A final, empty tag set,{}
, means “read from any member that matches the mode, ignoring tags.” MongoReplicaSetClient tries each set of tags in turn until it finds a set of tags with at least one matching member.See also
-
class
pymongo.read_preferences.
Secondary
(tag_sets=None, max_staleness=-1)¶ Secondary read preference.
- When directly connected to one mongod queries are allowed to standalone servers, to a replica set primary, or to replica set secondaries.
- When connected to a mongos queries are distributed among shard secondaries. An error is raised if no secondaries are available.
- When connected to a replica set queries are distributed among secondaries. An error is raised if no secondaries are available.
Parameters: - tag_sets: The
tag_sets
for this read preference. - max_staleness: (integer, in seconds) The maximum estimated length of time a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations. Default -1, meaning no maximum. If it is set, it must be at least 90 seconds.
-
document
¶ Read preference as a document.
-
max_staleness
¶ The maximum estimated length of time (in seconds) a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations, or -1 for no maximum.
-
min_wire_version
¶ The wire protocol version the server must support.
Some read preferences impose version requirements on all servers (e.g. maxStalenessSeconds requires MongoDB 3.4 / maxWireVersion 5).
All servers’ maxWireVersion must be at least this read preference’s min_wire_version, or the driver raises
ConfigurationError
.
-
mode
¶ The mode of this read preference instance.
-
mongos_mode
¶ The mongos mode of this read preference.
-
name
¶ The name of this read preference.
-
tag_sets
¶ Set
tag_sets
to a list of dictionaries like [{‘dc’: ‘ny’}] to read only from members whosedc
tag has the value"ny"
. To specify a priority-order for tag sets, provide a list of tag sets:[{'dc': 'ny'}, {'dc': 'la'}, {}]
. A final, empty tag set,{}
, means “read from any member that matches the mode, ignoring tags.” MongoReplicaSetClient tries each set of tags in turn until it finds a set of tags with at least one matching member.See also
-
class
pymongo.read_preferences.
SecondaryPreferred
(tag_sets=None, max_staleness=-1)¶ SecondaryPreferred read preference.
- When directly connected to one mongod queries are allowed to standalone servers, to a replica set primary, or to replica set secondaries.
- When connected to a mongos queries are distributed among shard secondaries, or the shard primary if no secondary is available.
- When connected to a replica set queries are distributed among secondaries, or the primary if no secondary is available.
Parameters: - tag_sets: The
tag_sets
for this read preference. - max_staleness: (integer, in seconds) The maximum estimated length of time a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations. Default -1, meaning no maximum. If it is set, it must be at least 90 seconds.
-
document
¶ Read preference as a document.
-
max_staleness
¶ The maximum estimated length of time (in seconds) a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations, or -1 for no maximum.
-
min_wire_version
¶ The wire protocol version the server must support.
Some read preferences impose version requirements on all servers (e.g. maxStalenessSeconds requires MongoDB 3.4 / maxWireVersion 5).
All servers’ maxWireVersion must be at least this read preference’s min_wire_version, or the driver raises
ConfigurationError
.
-
mode
¶ The mode of this read preference instance.
-
mongos_mode
¶ The mongos mode of this read preference.
-
name
¶ The name of this read preference.
-
tag_sets
¶ Set
tag_sets
to a list of dictionaries like [{‘dc’: ‘ny’}] to read only from members whosedc
tag has the value"ny"
. To specify a priority-order for tag sets, provide a list of tag sets:[{'dc': 'ny'}, {'dc': 'la'}, {}]
. A final, empty tag set,{}
, means “read from any member that matches the mode, ignoring tags.” MongoReplicaSetClient tries each set of tags in turn until it finds a set of tags with at least one matching member.See also
-
class
pymongo.read_preferences.
Nearest
(tag_sets=None, max_staleness=-1)¶ Nearest read preference.
- When directly connected to one mongod queries are allowed to standalone servers, to a replica set primary, or to replica set secondaries.
- When connected to a mongos queries are distributed among all members of a shard.
- When connected to a replica set queries are distributed among all members.
Parameters: - tag_sets: The
tag_sets
for this read preference. - max_staleness: (integer, in seconds) The maximum estimated length of time a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations. Default -1, meaning no maximum. If it is set, it must be at least 90 seconds.
-
document
¶ Read preference as a document.
-
max_staleness
¶ The maximum estimated length of time (in seconds) a replica set secondary can fall behind the primary in replication before it will no longer be selected for operations, or -1 for no maximum.
-
min_wire_version
¶ The wire protocol version the server must support.
Some read preferences impose version requirements on all servers (e.g. maxStalenessSeconds requires MongoDB 3.4 / maxWireVersion 5).
All servers’ maxWireVersion must be at least this read preference’s min_wire_version, or the driver raises
ConfigurationError
.
-
mode
¶ The mode of this read preference instance.
-
mongos_mode
¶ The mongos mode of this read preference.
-
name
¶ The name of this read preference.
-
tag_sets
¶ Set
tag_sets
to a list of dictionaries like [{‘dc’: ‘ny’}] to read only from members whosedc
tag has the value"ny"
. To specify a priority-order for tag sets, provide a list of tag sets:[{'dc': 'ny'}, {'dc': 'la'}, {}]
. A final, empty tag set,{}
, means “read from any member that matches the mode, ignoring tags.” MongoReplicaSetClient tries each set of tags in turn until it finds a set of tags with at least one matching member.See also
-
class
pymongo.read_preferences.
ReadPreference
¶ An enum that defines the read preference modes supported by PyMongo.
See High Availability and PyMongo for code examples.
A read preference is used in three cases:
MongoClient
connected to a single mongod:PRIMARY
: Queries are allowed if the server is standalone or a replica set primary.- All other modes allow queries to standalone servers, to a replica set primary, or to replica set secondaries.
MongoClient
initialized with thereplicaSet
option:PRIMARY
: Read from the primary. This is the default, and provides the strongest consistency. If no primary is available, raiseAutoReconnect
.PRIMARY_PREFERRED
: Read from the primary if available, or if there is none, read from a secondary.SECONDARY
: Read from a secondary. If no secondary is available, raiseAutoReconnect
.SECONDARY_PREFERRED
: Read from a secondary if available, otherwise from the primary.NEAREST
: Read from any member.
MongoClient
connected to a mongos, with a sharded cluster of replica sets:PRIMARY
: Read from the primary of the shard, or raiseOperationFailure
if there is none. This is the default.PRIMARY_PREFERRED
: Read from the primary of the shard, or if there is none, read from a secondary of the shard.SECONDARY
: Read from a secondary of the shard, or raiseOperationFailure
if there is none.SECONDARY_PREFERRED
: Read from a secondary of the shard if available, otherwise from the shard primary.NEAREST
: Read from any shard member.
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PRIMARY
= Primary()¶
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PRIMARY_PREFERRED
= PrimaryPreferred(tag_sets=None, max_staleness=-1)¶
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SECONDARY
= Secondary(tag_sets=None, max_staleness=-1)¶
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SECONDARY_PREFERRED
= SecondaryPreferred(tag_sets=None, max_staleness=-1)¶
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NEAREST
= Nearest(tag_sets=None, max_staleness=-1)¶